1. Field of the Invention
The present invention relates to a positive resist composition suitably used in the ultramicrolithography process for producing, for example, VLSI or high-capacity microchip or in other photofabrication processes, and a pattern forming method using the composition. More specifically, the present invention relates to a positive resist composition capable of forming a highly refined pattern with use of KrF excimer laser light, electron beam, EUV light or the like, and a pattern forming method using the composition, that is, the present invention relates to a positive resist composition suitably usable for fine processing of a semiconductor device, where KrF excimer laser light, electron beam or EUV light is used, and a pattern forming method using the composition.
2. Background Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X ray or EUV light is proceeding.
The lithography using electron beam or EUV light is positioned as a next-generation or next-next-generation pattern formation technique and a positive resist with high sensitivity and high resolution is being demanded. In particular, the elevation of sensitivity for shortening the wafer processing time is very important but in the positive resist for use with electron beam or EUV, when higher elevation is sought for, not only reduction of resolution but also worsening of line edge roughness are brought about and development of a resist satisfying these properties at the same time is strongly demanded. The line edge roughness as used herein means that the resist edge at the interface between the pattern and the substrate irregularly fluctuates in the direction perpendicular to the line direction due to the resist property and when the pattern is viewed from right above, the edge gives an uneven appearance. This unevenness is transferred by the etching step using the resist as a mask and causes deterioration of electric property, giving rise to decrease in the yield. Particularly, in the ultrafine region of 0.25 μm or less, the improvement of line edge roughness is an essential problem to be solved. The high sensitivity is in a trade-off relationship with high resolution, good pattern profile and good line edge roughness and it is very important how to satisfy these matters at the same time.
Furthermore, also in the lithography using X-ray or EUV light, it is similarly very important to satisfy high sensitivity, surface roughness and the like at the same time, and this problem needs to be solved.
As for the resist suitable for the lithography process using electron beam, X-ray or EUV light, a chemical amplification-type resist utilizing an acid catalytic reaction is mainly used from the standpoint of elevating the sensitivity and in the case of a positive resist, a chemical amplification-type resist composition mainly comprising an acid generator and a phenolic polymer which is insoluble or sparingly soluble in an alkali developer but becomes soluble in an alkali developer under the action of an acid (hereinafter simply referred to as a “phenolic acid-decomposable resin”), is being effectively used.
With respect to the positive resist for use with electron beam, X-ray or EUV, some resist compositions containing a phenolic acid-decomposable resin have been heretofore known (see, for example, Patent Documents 1 and 2: JP-A-2003-345023 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-2002-55457, respectively).
However, it is impossible at present by any of these combinations to satisfy high resolution and good line edge roughness in the ultrafine region at the same time.
Furthermore, unlike a conventional light source, in the case of irradiating a high-energy ray such as EUV light, an outgassing problem becomes prominent, where a compound in the resist film is destroyed by fragmentation and volatizes as a low molecular component during exposure to contaminate the environment in the exposure apparatus. Various studies are being made for the reduction of outgassing and various techniques are attempted, such as a technique of providing a topcoat layer to suppress the volatilization of a low molecular compound (see, for example, Patent Document 3: European Patent 1,480,078) or a technique of adding a radical trapping agent for suppressing the decomposition of a polymer (see, for example, Patent Document 4: U.S. Pat. No. 6,680,157). Thus, an effort for reducing the outgassing is demanded also in terms of the acid generator.